Unit-flow certificate for project duration
= Unit-flow certificate for project duration
A feasible timetable with finish time $T$ and a unit flow carried on a precedence path of total duration $T$ certify optimality. Summing the inequalities $t_j-t_i\geq\tau_i$ along that path proves every schedule needs at least $T$, while the timetable attains it.
// Target: computer-science.bigb